1. Field of the Disclosure
The present disclosure relates generally to toner cartridges used in electrophotographic imaging devices such as a printer or multifunction device having printing capability, and in particular to a pressure equalization system used for toner cartridges.
2. Description of the Related Art
In toner cartridge design, it is now common practice to separate the longer lived components from those having a shorter life. This has lead to having the longer lived developing components such as the developer roll, toner adder rolls, doctor blades, the foregoing are also referred to as a developing unit, photoconductive drums, cleaning and charge rollers and a waste bin to be in separate assemblies from the toner cartridge. The toner supply, which is consumed relatively quickly in comparison to the previously described components, is provided in a reservoir in a separate toner cartridge that mates with the developer unit. The toner cartridge has a reduced number of components and is often referred to as a toner bottle even though it is more than a mere bottle for holding toner.
To deliver the toner from the toner cartridge to the developer unit, an auger in the toner cartridge may be used to feed toner from the toner cartridge via an exit port on the toner cartridge into an entry port on the developer unit and into a second auger that disperses the toner within the developer unit. As the toner is drawn out of the cartridge unit, it is augured through a shutter used for sealing the exit port of the toner cartridge when it is not inserted in the imaging apparatus.
While moving toner through the restriction formed by the shutter, auger and exit port, the opening from the exit port into the toner reservoir in the toner cartridge is relatively air tight. A low pressure condition or vacuum-like condition is created in the toner cartridge as toner is removed as air cannot enter to fill the void. If the toner cartridge were viewed as being a pump supplying toner from the toner reservoir, this low pressure condition would be analogous to cavitation in a pump.
In the same manner, as toner is augured into the developer unit, it passes through another shutter used to prevent toner from escaping the developer when the cartridge is not installed in the printer. This opening restricts airflow, therefore, as toner is dispensed into the developer unit, air must be displaced and a positive pressure is created in the developer unit. Further, the rotation of the developer roll causes the developer unit to ingest air further increasing the positive pressure in the developer unit. Toner being delivered from the toner cartridge to the developer unit must travel against this positive pressure gradient. This causes a significant reduction in the flow rate of the toner which can lead to failures such as incorrect cartridge empty indications, developer packing, or developer unit starvation.
This described pressure differential between the toner cartridge and developer unit necessitated that a vent be used to equalize the pressure between the developer unit and the toner cartridge. Previous venting methods for the toner cartridge included having a vent hole through the toner cartridge into the toner reservoir. Labyrinth type vent plugs, vent plugs of a porous material, and even foam tape have been used to vent air into the toner cartridge while preventing toner from escaping the toner cartridge through the vent hole. However, these methods were not successful in equalizing the pressure between the developer unit and the toner cartridge as these vent plug designs and foams tended to become clogged with toner. Further, even with the vent plugs being clear and the toner cartridge no longer in a low pressure state, venting of the higher pressure air in the developer unit back into the toner cartridge was problematic due to the restriction caused by the shutter for the exit port of the toner cartridge still causing the aforementioned pressure differential to exist between the toner cartridge and the developer unit.
In other previous toner cartridge designs, the developer unit and cartridge unit were permanently mated together so there was open fluid communications between the developer unit and the toner reservoir so that the entire system would become pressurized due to the ingestion of air caused by the rotation of the developer roll. In some cases, an internal vent was provided within the permanently mated developer unit and toner reservoir. These cartridges vented the higher internal air pressure to the atmosphere. The vent was typically made out of a porous woven materials, such as GORTEX® or VERSAPORE®, or felt. These venting methods were all designed around the principle of letting air out of the cartridge while filtering and restricting toner particles from escaping. They also required the filter to be placed in a position on the cartridge that was not buried under toner. However, faster process speeds, larger toner loads, as well as separating the toner cartridge and developer unit make these methods inadequate.
To solve the pressure differential problem, it would be advantageous to have a pressure equalization system to give air a path to move from a high pressure developer unit to a low pressure toner cartridge through the exit port of the toner cartridge. It would be a further advantage to have such a ducting system be sealable to prevent toner from escaping the toner cartridge during shipping, storage, and when removed from the imaging apparatus. It would be a further advantage to be able to provide a high rate of toner delivery that helps avoid a number of previously mentioned toner delivery failures.